Continuously variable transmissions usually have one variator for ratio adjustment which comprises a first cone pulley pair upon an input shaft and a second cone pulley pair upon an output shaft and belt means, such as a movable articulated chain or a pushing link band, rotating between the cone pulley pairs. Each cone pulley pair consists of a first pulley, stationary in an axial direction, and a second cone pulley, movable in an axial direction. The input shaft of the variator is usually designated as a primary shaft and, accordingly, the first cone pulley pair as a primary pulley pair. Similarly the output shaft of the variator is customarily designated as a secondary shaft and the second cone pulley pair as a secondary pulley pair. The primary pulley and secondary pulley and thus the ratio therebetween are adjusted by a pressure medium. To this end, an electrohydraulic control unit controls the pressure level of the adjustment spaces of the primary and secondary pulleys via electromagnetic actuators and hydraulic valves. The pressure medium is usually conveyed by the electrohydraulic transmission control, via ducts located in the transmission housing, to an axial hole of the primary shaft or the secondary shaft and from there to a pressure chamber of the primary pulley or the secondary pulley, the required hole diameter or hole cross-section resulting from the volume adjustment needed by the variator.
DE-A-195 33 995 has disclosed a continuously variable transmission where the primary shaft end on the input side has a first axial hole for supplying pressure to a clutch, and the primary shaft end opposite to the input has a second axial hole for supplying the primary pressure. The primary pressure is supplied to said second axial hole of the primary shaft from a duct situated in the transmission housing, via a sleeve firmly plugged in the duct discharge in the transmission housing, which sleeve extends into the second axial hole of the primary shaft. A single rectangular ring is provided for sealing between the stationary sleeve and the rotating primary shaft.
In DE-A-199 32 339 a continuously variable transmission has been disclosed where an axial hole, designed as a stepped hole is provided in the primary shaft through which the primary pressure is conveyed to the pressure chamber of the primary pulley and also a lubrication pressure independent of the primary pressure is conveyed to another component. For the supply of the pressurized oil needed to adjust the primary pulley, a primary pressure duct is provided in the transmission housing, between the primary pulley and a housing cover adjacent the primary shaft, which extends substantially radially to the center of the primary shaft and discharges on an inner cover which ensures sealing between cover and the inner diameter of the large hole of the axial stepped hole of the primary shaft. A single rectangular ring is provided as a sealing element between the stationary inner cover and the rotating primary shaft. The housing cover further has a tubular projection which serves as a duct for lubrication pressure and sinks down to the small hole of the stepped hole of the axial primary shaft sealing it against the large hole of the stepped hole of the axial primary shaft. To this end, a rectangular ring is situated on the outer diameter of a dipping projection end. The lubrication oil is passed, via an inner hole of the tubular projection of the cover, into the small hole of the axial stepped hole of the primary shaft and from there to one other component. Therefore, primary pressure abuts on the annular space between the outer diameter of the tubular cover projection and the inner diameter of the large hole of the axial stepped hole of the primary shaft while lubrication pressure abuts on the small hole of the axial stepped hole of the primary shaft.
A failure of the rectangular ring, which separates the two pressure areas from each other as a consequence of the great leakage on the rectangular ring, can result, on one hand, in failure of the transmission when the second component is loaded with too high a pressure level (primary pressure) and, on the other hand, also to critical driving states when undesirable lubrication pressure is introduced in the pressure chamber of the primary pulley thus triggering or preventing an adjustment of the variator, or when the second component is a shifting element and the primary pressure is introduced in the piston chamber of this clutch thereby triggering an undesirable shifting operation.
DE-A-196 03 598 describes a secondary set of a variator for a continuously variable transmission where the secondary shaft has an axial hole through which the secondary pressure to a secondary pressure chamber and a lubrication pressure independent of the secondary pressure to a pressure compensation space of the secondary pulley are both passed. The pressurized oil is supplied to the secondary pressure chamber from a duct of the transmission housing via a pipe inserted in the transmission housing and extending into the axial secondary shaft hole. The lubrication oil is supplied for dynamic pressure compensation of the secondary set, via an annular space, between the outer diameter of the pipe and the inner diameter of the axial secondary shaft hole. A low friction bearing plugged between the stationary pipe and the axial secondary shaft hole is provided in the axial secondary shaft hole for two-way sealing of both pressure supplies.
Excessive leakage on the low friction bearing which separates the two pressure supplied in the axial secondary shaft hole from each other on the pressure side, can also result here in function interruptions of the variator when the pressure-compensation space of the secondary pulley is undesirably loaded with a high pressure level.